1. Field of the Invention
The invention generally relates to a valve which may be used as a master valve for a production well, or alternatively as a safety or blowout preventer valve between a tubing head and a production (Christmas) tree. The invention also generally relates to valve apparatus providing complete control over a well during installation or workover of tubing in an oil or gas well.
More specifically, the invention, in its blowout preventer embodiment, is directed for use on offshore production platforms where a plurality of producing oil wells are disposed in close proximity to one another and where there is an emergency need to simultaneously shut in all the producing wells rapidly, safety, reliably, and economically while facilitating rapid resumption of production after the emergency has passed.
The invention may also serve as a substitute for a master valve in production wells where a vertical production tree is eliminated in favor of horizontal plane apparatus.
2. Description of the Prior Art
On marine production platforms there are often many producing wells in close proximity to one another. Each of the wells typically has a production wellhead from which production tubing extends from the well. The wellhead typically has a production or "Christmas" tree connected to it for controlling the gas or fluid flowing in the production tubing during production of the well. A master gate valve disposed in each production tree may be closed to shut off flow from the well, but such gate valves may be difficult to close rapidly during an emergency due to their location, and indeed may not be available as where the production tree is removed from the wellhead during workover of the well.
Downhole saftey valves may also be provided in each of the producing wells; but there is always the danger that a downhole safety valve may not be operable or in place during workover of the well. As indicated above, during workover, the production tree may have been removed in order to install a blowout preventer stack atop the production wellhead for control of the well during workover. Such a blowout preventer stack is of the kind used typically in drilling operations and includes one or more ram-type blowout preventers and an annular blowout preventer. Until the blowout preventer is installed on the production wellhead and connected to its controls, well control in the past for the well has depended upon remotely installed plugs in the well. Such plugs have not always been reliable.
During an emergency on an offshore platform, for example, where a fire or leaking gas or fluid from one production tree endangers all of the wells and indeed the platform itself, there has developed the need for an apparatus and method for its installation and refurbishing which may be used to rapidly close off the flow path of the production tubing in each of the wells.
As indicated above, a shear ram blowout preventer similar to those used in marine blowout preventer stacks for drilling operations could be a candidate for satisfying such a need. The use of a shear ram blowout preventer has a major disadvantage in that the tubing above the tubing hanger must be replaced after it has been sheared before production can be resumed. Shear ram blowout preventers crush the production tubing which must be replaced before the well can be put back into operation. In order to replace the crushed tubing, the production tree must be removed and a drilling blowout preventer and rig installed in order to remove the damaged tubing and replace it with new tubing.
Another disadvantage of using a shear ram blowout preventer similar to that used in drilling operations is that after the preventer crushes and shears the tubing, the well can only be controlled by pumping mud into it to control the pressure in the well. A plug typically cannot be installed through the tubing which has been crushed during the shearing by the preventer.